Highly flexible stent

ABSTRACT

A stent includes wavy-line pattern bodies having a wavy-line pattern and arranged side-by-side in an axial direction LD, and coiled elements arranged between the wavy-line pattern bodies adjacent and extending in a spiral manner around an axis. All apices on opposite sides of the wavy-line pattern of the wavy-line pattern bodies that are adjacent are connected by way of the coiled element. When viewing in a radial direction RD, a circular direction CD of the wavy-line pattern bodies is inclined with respect to the radial direction RD, and a winding direction of one of the coiled elements located at one side in the axial direction LD with respect to the wavy-line pattern bodies and a winding direction of one other of the coiled elements located at the other side in the axial direction LD are opposite.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of co-pending application Ser. No.14/408,203, filed on Dec. 15, 2014, which is a U.S. National Stage ofInternational Application No. PCT/JP2014/071469 filed on Aug. 15, 2014,for which priority is claimed under 35 U.S.C. §120; and this applicationclaims priority of Application No. 2014-029933 filed in Japan on Feb.19, 2014 and Application No. 2014/165104 filed in Japan on August 154,2014 under 35 U.S.C. §119; the entire contents of all of which arehereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to a highly flexible stent placed in aluminal structure of a living body in order to expand lumen.

BACKGROUND ART

In a biological organ having a luminal structure such as blood vessels,the trachea and the intestines, when stenosis occurs therein, acylinder-shaped stent with mesh pattern is used in order to securepatency at a site of pathology by expanding an inner cavity at anarrowed part. These biological organs often have bent or taperedstructures locally (i.e. a tubular structure of which sectionaldiameters of the inner cavity differ locally in an axial direction).Therefore, a stent having higher conformability has been desired whichcan flexibly adapt to such a complex vessel structure. Furthermore, inrecent years, stents have come to also be employed for the treatment ofcerebral blood vessels. Among tubular organs in a living body, thecerebral vessel system has a more complex structure. The cerebral vesselsystem has many bent sites and sites having tapered structures.Therefore, stents with particularly higher conformability have beenrequired therein.

For the purpose of realizing a stent with higher conformability, the twokinds of mechanical flexibilities of a longitudinal axis direction (in acentral axis direction) and a radial direction (a directionperpendicular to the longitudinal direction) of the stent are said to beimportant. Thereamong, the flexibility in a longitudinal axis directionrefers to stiffness with respect to bending along a longitudinal axisdirection or the ease of bending. The flexibility in a radial directionrefers to stiffness with respect to expansion and contraction along adirection perpendicular to a longitudinal axis direction or the ease ofexpansion and contraction. The mechanical flexibility in a longitudinalaxis direction is a property that is necessary for a stent to beflexibly bent along a longitudinal axis direction to allow adapting to abent site of a tubular organ in a body. The mechanical flexibility in aradial direction is a property that is necessary for making the radiusof a stent flexibly differ following the shape of an outer wall of aluminal structure of a tubular organ in a body so that the stent is intight contact with the outer wall of the luminal structure. Morespecifically, regarding the latter, the flexibility in the radialdirection, with consideration of not only a stent having lowerstiffness, but also the stent being placed in an organ in a body havinga tapered structure, it is necessary for a stent to have a propertywhereby the expansive force of the stent does not change greatlydepending on local changes in sectional diameters of the inner cavity ata site having a tapered structure.

The structures of a stent are generally classified into the two types ofopen cell structures and closed cell structures. Since a stent having anopen cell structure exerts remarkable mechanical flexibility in thelongitudinal axis direction, the conformability is high and thus theopen cell structures have been recognized as being effective for a stentstructure that is placed in a tortuous tubular organ. However, for suchan open cell structure, since a part of a strut of the stent mayprotrude radially outward in a flared shape when bent, there is a riskof damaging the tissue of a tubular organ in a body such as bloodvessels when the stent is placed therein. On the other hand, regardingstents having a closed cell structure, there are those having closedcell structures that allow for a partial repositioning of a stent duringoperation, which had been difficult with stents of open cell structures,and stents having closed cell structures that allow for fullrepositioning of the stent during operation.

For such a closed cell structure, although there is no risk of the strutof the stent protruding radially outward such as a stent having an opencell structure, the flexibility of the structure tends to be lacking.Therefore, there has been a risk of inhibiting the flow of liquid suchas blood in tubular organs from flowing due to a stent buckling whenapplying the stent having a closed cell structure to a bent tubularorgan. Furthermore, structurally speaking, since the stent having aclosed cell structure is inferior to the stent having an open cellstructure in terms of a reduction in diameter, the stent having a closedcell structure cannot handle placement of a stent into a tubular organof small diameter of around 2 mm, a result of which there has been arisk of damaging a body tissue.

In order to solve such problems, a spiral stent has been devised as atechnology exhibiting high flexibility while being a stent having aclosed cell structure (for example, refer to Japanese Unexamined PatentApplication (Translation of PCT Publication), Publication No.2010-535075.) The stent disclosed in Japanese Unexamined PatentApplication (Translation of PCT Publication), Publication No.2010-535075 includes spiral circular bodies having a wavy-line patternand coiled elements connecting adjacent circular bodies in an expandedstate.

Patent Document 1: Japanese Unexamined Patent Application (Translationof PCT Publication), Publication No. 2010-535075

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

However, after a stent has been placed in a superficial femoral artery,for example, inner and outer rotational actions of a femoral area causeinner and outer rotations of a blood vessel. The stent in the bloodvessel thereby is also distorted in an inner rotational direction and anouter rotational direction. However, in Japanese Unexamined PatentApplication (Translation of PCT Publication), Publication No.2010-535075, since the deformed form of a stent differs depending on adirection in which the stent is distorted, distorted deformations of thestent due to the inner and outer rotations of the blood vessel becomeuneven, for example. Therefore, a difference arises in load on bloodvessel walls from stents between left and right blood vessels. Inparticular, since there are differences among individuals in ratios ofinner and outer rotations between left and right legs, for a patient whofrequently performs an inner rotation of both legs, for example, in acase in which the stent is a stent that follows an inner rotation of theright leg, the stent cannot follow the inner rotation of the left leg.For this reason, since the load on the blood vessel walls from the stentdiffers between the left and right legs, even if treatment is done withthe same stent, the rate of incurring a complicating disease after thestent being placed differs between the left and right legs.

Furthermore, since there are both inner and outer rotations for one leg,for example, the right leg, as described above, a stent that follows aninner rotation well cannot follow an outer rotation well. Due to theabovementioned problem, the following clinical problems occur:

(1) the risk of the stent being broken increases due to repetitivedistorting loading; and

(2) the risk of a blood vessel wall being damaged increases due tostress being applied intensively from a stent at a local portionthereof.

Regarding the stent of Japanese Unexamined Patent Application(Translation of PCT Publication), Publication No. 2010-535075, thecoiled elements can be assumed approximately as a portion of thestructure of a wound spring. Furthermore, if distorting loading isapplied to the stent, deformation is caused intensively at the coiledelements. For this reason, it is possible to predict a reaction of adistorted deformation of this stent by considering of the distorteddeformation of the spring structure of the coiled elements.

Here, distorted deformation behaviors in a case of assuming adeformation of a coiled element in an expanded state of the stent ofJapanese Unexamined Patent Application (Translation of PCT Publication),Publication No. 2010-535075 as a part of a left-hand spring structureare illustrated in FIGS. 18B, 18C, 18E, and 18F. As illustrated in FIGS.18B and 18E, when a distortion in a left-hand direction is applied to aleft-hand spring, a force acts so as to be pulled in a perpendiculardirection with respect to a cross section of an element wire of thespring. For this reason, as illustrated in FIGS. 18C and 18F, theelement wire is deformed so as to be wound in the circumferentialdirection thereof and exhibits a behavior of being radially reduced inthe radial direction. On the other hand, when a distortion in aright-hand direction is applied, a force acts so as to be compressed ina perpendicular direction with respect to the cross section of theelement wire of the spring. For this reason, as illustrated in FIGS. 18Aand 18D, the element wire is deformed so as to be pulled away in thecircumferential direction thereof and exhibits a behavior of the outsidediameter being expanded in a radial direction as a result.

Since the stent of Japanese Unexamined Patent Application (Translationof PCT Publication), Publication No. 2010-535075 is composed of a springbody, when distortion in a left or right direction is applied, itexhibits a behavior similar to the abovementioned distorted deformationof the wound spring. Due to this distorted deformation behavior, asubstantial difference in deformation amounts in the radial direction ofthe stent between the distorted deformations in the left and rightdirection appears, whereby the load to blood vessel walls differs.Therefore, even when performing treatment with the same stent asdescribe above, treatment results may differ depending on target sitesfor treatment or difference among individuals.

Therefore, it is an object of the present invention to provide a highlyflexible stent that can suppress a deformation amount in the radialdirection of the stent with respect to a distortion load.

Means for Solving the Problems

The present invention relates to a highly flexible stent including: aplurality of wavy-line pattern bodies having a wavy-line pattern andarranged side-by-side in an axial direction; and a plurality of coiledelements arranged between the wavy-line pattern bodies that are adjacentand extending in a spiral manner around an axis, in which all apices onopposite sides of the wavy-line pattern of the wavy-line pattern bodiesthat are adjacent are connected by way of the coiled elements, in which,when viewing in a radial direction perpendicular to the axial direction,a circular direction of the wavy-line pattern bodies is inclined withrespect to the radial direction, and in which a winding direction of oneof the coiled elements located at one side in the axial direction withrespect to the wavy-line pattern bodies and a winding direction of oneother of the coiled elements located at the other side in the axialdirection are opposite.

An angle at which the circular direction of the wavy-line pattern bodiesinclines with respect to the radial direction may be 30° to 60°.

The wavy-line pattern bodies may form a circular body by connecting, ina circumferential direction, a plurality of waveform elements ofsubstantially V-shape made by coupling two leg portions at an apex, andthe length of the one of the coiled elements may be longer than thelength of the leg portion and the length of the one other of the coiledelements may be shorter than the length of the leg portion.

The length of the one of the coiled elements may be no more than 1.5times the length of the leg portion.

The wavy-line pattern bodies may be non-continuous in a circumferentialdirection and may not form a circular body, and may have a shape inwhich one or a plurality of struts that constitutes the wavy-linepattern bodies is omitted, as compared with the wavy-line pattern bodiesthat form a circular body.

A cross sectional shape may be a substantially triangular shape.

Effects of the Invention

According to the present invention, it is possible to provide a highlyflexible stent that can suppress a deformation amount in the radialdirection of the stent with respect to a distortion load.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a highly flexible stent in anunloaded state according to a first embodiment of the present invention;

FIG. 2 is a developed view showing a highly flexible stent in anunloaded state according to a first embodiment of the present inventionthat is virtually expanded into a plane;

FIG. 3 is a partially enlarged view of the stent shown in FIG. 2;

FIG. 4 is a partially enlarged view of the stent shown in FIG. 3;

FIG. 5 provides illustrative views showing the matter of deformationoccurring at an apex of a waveform element of the circular body of astent when the stent is radially reduced;

FIG. 6A is a schematic view showing a deformation state of a waveformelement during diameter reduction in a case in which a slit is notprovided at an apex of a waveform element of the circular body of astent;

FIG. 6B is a schematic view showing a deformation state of a waveformelement during diameter reduction in a case in which a slit is notprovided at an apex of a waveform element of the circular body of astent;

FIG. 7A is a schematic view showing a deformation state of a waveformelement during diameter reduction in a case in which a slit is providedat an apex of a waveform element of the circular body of a stent;

FIG. 7B is a schematic view showing a deformation state of a waveformelement during diameter reduction in a case in which a slit is providedat an apex of a waveform element of the circular body of a stent;

FIG. 8 is a partially enlarged view showing a first embodiment of anapex of a waveform element of the circular body of the stent;

FIG. 9 is a partially enlarged view showing a second embodiment of anapex of a waveform element of the circular body of the stent;

FIG. 10 is a partially enlarged view showing a third embodiment of anapex of a waveform element of the circular body of the stent;

FIG. 11A shows a central axis of a cross section of a stent and a sideview of a blood vessel;

FIG. 11B is a schematic view of a cross section of a stent where acentral axis is not displaced;

FIG. 11C is a schematic view of a cross section of a stent where acentral axis is displaced;

FIG. 12 is a schematic view showing a malapposition;

FIG. 13 is a schematic view of a developed view of a highly flexiblestent in an unloaded state according to a first embodiment of thepresent invention;

FIG. 14 is a schematic view showing the behavior of a coiled element andthe center of the figure when the stent shown in FIG. 13 is bent;

FIG. 15 is a schematic view showing the behavior of the center in thefigure of a cross section of the bent stent;

FIG. 16 is a schematic view showing the behavior in a case in which adistortion in a right-hand direction is applied to the stent shown inFIG. 13;

FIG. 17 is a schematic view showing the behavior in a case in which adistortion in a left-hand direction is applied to the stent shown inFIG. 13;

FIGS. 18A, 18B, 18C, 18D,18E, and 18F is a schematic view showing thebehavior of a distorted deformation in a case of assuming a deformationwith a coiled element of a stent as a part of a left-hand springstructure;

FIG. 19 is a developed view of a conventional stent in which a circulardirection of a circular body is not inclined with respect to a radialdirection;

FIG. 20 is a developed view showing a state after bending deformationbeing applied to the stent shown in FIG. 19;

FIG. 21 is a developed view showing the highly flexible stent accordingto a second embodiment of the present invention to be virtually expandedinto a plane;

FIG. 22 is a developed view showing the highly flexible stent accordingto a first modified example of a second embodiment of the presentinvention to be virtually expanded into a plane;

FIG. 23 is a developed view showing the highly flexible stent accordingto a second modified example of a second embodiment of the presentinvention to be virtually expanded into a plane;

FIG. 24 is a developed view showing the highly flexible stent accordingto a third modified example of a second embodiment of the presentinvention to be virtually expanded into a plane;

FIG. 25 is a developed view showing the highly flexible stent accordingto a fourth modified example of a second embodiment of the presentinvention to be virtually expanded into a plane;

FIG. 26 is a developed view showing the highly flexible stent accordingto a fifth modified example of a second embodiment of the presentinvention to be virtually expanded into a plane;

FIG. 27 is a developed view showing the highly flexible stent accordingto a sixth modified example of a second embodiment of the presentinvention to be virtually expanded into a plane;

FIG. 28 is a developed view showing the highly flexible stent accordingto a seventh modified example of a second embodiment of the presentinvention to be virtually expanded into a plane;

FIG. 29 is a developed view showing the highly flexible stent accordingto a third embodiment of the present invention to be virtually expandedinto a plane;

FIG. 30 is a developed view showing the highly flexible stent accordingto a fourth embodiment of the present invention to be virtually expandedinto a plane;

FIG. 31 is a developed view showing the highly flexible stent accordingto a fifth embodiment of the present invention to be virtually expandedinto a plane;

FIGS. 32A, 32B, 32C, and 32D are views showing the behavior of a highlyflexible stent of the present invention being pushed out from a catheterand expanded;

FIG. 33 is a view showing a state in which the highly flexible stent ofthe present invention traps a blood clot;

FIG. 34 is a perspective view of a highly flexible stent according to asixth embodiment of the present invention;

FIG. 35 is a view in which the highly flexible stent shown in FIG. 34 isseen in an axial direction;

FIG. 36 is a developed view showing that a highly flexible stentaccording to a seventh embodiment of the present invention is virtuallyexpanded into a plane;

FIG. 37 is a developed view showing various modified examples of a coilelement;

FIG. 38 is a view showing a modified example of a shape of a connectingportion of a coiled element and an apex of a circular body (viewcorresponding to FIG. 4);

FIG. 39 is a cross sectional view showing a connecting portion of ahighly flexible stent of the present invention and a guide wire; and

FIG. 40 is a cross sectional view showing a tip portion of a highlyflexible stent of the present invention.

EXPLANATION OF REFERENCE NUMERALS

-   -   11, 11A, 11B, 11C, 11D, 11E, 11F stent (highly flexible stent)    -   13 circular body (wavy-line pattern body)    -   15 coiled element    -   15L other coiled element    -   15R one coiled element    -   17 waveform element    -   17 a leg portion    -   17 b apex    -   19 knob portion    -   21 slit    -   LD axial direction (longitudinal axis direction)    -   RD radial direction    -   CD circular direction    -   θ angle inclined

PREFERRED MODE FOR CARRYING OUT THE INVENTION

In the following, a first embodiment of a highly flexible stentaccording to the present invention is described with reference to thedrawings. With reference to FIGS. 1 to 3, first, the overallconfiguration of a highly flexible stent 11 according to the firstembodiment of the present invention is described. FIG. 1 is aperspective view of a highly flexible stent according to the firstembodiment of the present invention in an unloaded state. FIG. 2 is adeveloped view showing the highly flexible stent according to the firstembodiment of the present invention in an unloaded state to be virtuallyexpanded into a plane. FIG. 3 is a partially enlarged view of the stentshown in FIG. 2.

As illustrated in detail in FIG. 1, the stent 11 is of a substantiallycylindrical shape. A peripheral wall of the stent 11 has a structure ofa mesh pattern in which a plurality of closed cells having a congruentshape surrounded by wire-shaped materials is covering a circumferentialdirection. In FIG. 2, for the purpose of facilitating understanding ofthe structure of the stent 11, the stent 11 is illustrated in a stateexpanded in a plane. Furthermore, in FIG. 2, in order to show the cyclicnature of the mesh pattern, the mesh pattern is shown in such a mannerthat it is virtually repeated more than an actual developed statethereof. In the present specification, the peripheral wall of the stent11 refers to a part that separates the inside from the outside of acylinder with a substantially cylindrical shape of the stent 11.Furthermore, the term “cell” also refers to an opening or a compartmentthat is a part enclosed by the wire-shaped material forming the meshpattern of the stent 11.

The stent 11 is formed of material having biocompatibility such asstainless steel, tantalum, platinum, gold, cobalt, titanium, or alloysof these. It is particularly preferable for the stent 11 to be formed ofmaterials having a super elastic property such as a nickel titaniumalloy.

The stent 11 includes a plurality of circular bodies 13, as a wavy-linepattern body, that is arranged in a longitudinal axis direction LD (i.e.a center axis direction) and a plurality of coiled elements 15 that isarranged between the adjacent circular bodies 13 in the longitudinalaxis direction LD. As shown in FIG. 3, the circular bodies 13 include awavy-line pattern that is formed by connecting, in a circumferentialdirection, a plurality of waveform elements 17 of substantially V-shapemade by coupling two leg portions 17 a at an apex 17 b. Morespecifically, the waveform elements 17 of substantially V-shape areconnected in a state in which the apices 17 b are arranged alternatelyat the opposite sides.

When viewing in a radial direction RD perpendicular to the axialdirection LD, a circular direction CD of the circular bodies 13 isinclined with respect to the radial direction RD. The angle θ at whichthe circular direction CD of the circular bodies 13 is inclined withrespect to the radial direction RD is 30° to 60°, for example.

Both ends of each of the coiled elements 15 are connected with theapices 17 b, respectively, at opposite sides of two adjacent circularbodies 13. It should be noted that all of the apices 17 b at theopposite sides of the adjacent circular bodies 13 are connected to eachother by the coiled element 15. The stent 11 has a so-called closed cellstructure. In other words, the two apices 17 b that are arranged to beadjacent to each other along the wavy-line pattern among the threeapices 17 b connected to each other via the leg portions 17 a along thewavy-line pattern at one of the circular bodies 13 that are adjacentthereto are respectively connected with the two apices that are arrangedto be adjacent to each other along the wavy-line pattern among the threeapices connected to each other via the leg portions 17 a along thewavy-line pattern at the other one of the circular bodies 13 that areadjacent thereto by way of the coiled elements 15, to form cells. Then,all of the apices 17 b of the wavy-line pattern of each of the coiledbodies 13 are shared with three cells.

The plurality of coiled elements 15 is arranged at regular intervalsalong the circular direction CD of the circular bodies 13. Each of theplurality of coiled elements 15 extends in a spiral manner around thecenter axis. As shown in FIG. 3, the winding direction (right-handed) ofone coiled element 15 (15R) located at one side in the axial directionLD with respect to the circular body 13 and the winding direction(left-handed) of the other coiled element 15 (15L) located at the otherside in the axial direction LD are opposite. The length of the onecoiled element 15R is longer than the length of the leg portion 17 a,but no more than 1.5 times the length of the leg portion 17 a. Thelength of the other coiled element 15L is shorter than the length of theleg portion 17 a.

FIG. 4 is a partially enlarged view of the stent shown in FIG. 3. FIG. 5is an illustrative view showing a matter of deformation occurring at anapex of a waveform element of a circular body of a stent when the stentis radially reduced. FIG. 6A is a schematic view showing a deformationstate of a waveform element during diameter reduction in a case in whicha slit is not provided at an apex of a waveform element of a circularbody of a stent. FIG. 6B is a schematic view showing a deformation stateof a waveform element during diameter reduction in a case in which aslit is not provided at an apex of a waveform element of a circular bodyof a stent. FIG. 7A is a schematic view showing a deformation state of awaveform element during diameter reduction in a case in which a slit isprovided at an apex of a waveform element of a circular body of a stent.FIG. 7B is a schematic view showing a deformation state of a waveformelement during diameter reduction in a case in which a slit is providedat an apex of a waveform element of the circular body of a stent.

As illustrated in FIGS. 4 and 5, a knob portion 19 is formed at the apex17 b of the waveform element 17. The knob portion 19 includes anextension portion 19 a extending linearly in the longitudinal axisdirection LD and a substantially semicircle portion (tip portion) 19 bformed at a tip thereof. The extension portion 19 a has a width broaderthan the width of the coiled elements 15. Furthermore, at the apex 17 bof the waveform element 17, a slit 21 is formed that extends in thelongitudinal axis direction LD from an inner peripheral portion (avalley portion side of the left side of the waveform element 17 ofsubstantially V-shape in FIG. 4). Therefore, two leg portions 17 a areconnected to the substantially semicircle portion 19 b of the knobportion 19 and a region of the extension portion 19 a in which a slit 21is not provided, via linear portions extending substantially in parallelin the longitudinal axis direction LD. It should be noted that, althoughit is preferable for the tip portion 19 b to be substantially asemicircle portion, it may not be a substantially semicircle portion(not illustrated).

A curve portion 15 a is formed at both ends of each of the coiledelements 15. Both ends of each of the coiled elements 15 arerespectively connected to the apices 17 b (more specifically, the knobportion 19) at the opposite sides of two adjacent circular bodies 13 viathe curve portion 15 a. As shown in FIG. 4, the curve portions 15 a ofboth ends of the coiled elements 15 have an arc-like shape. Thetangential direction of the coiled elements 15 at a connecting end ofthe coiled element 15 and the apex 17 b of the wavy-line pattern of thecircular body 13 coincides with the longitudinal axis direction LD.

The center in the width direction of an end of the coiled element 15 andan apex (the center in the width direction) of the apex 17 b of thecircular body 13 are displaced from each other (do not match). An endedge in the width direction of the end of the coiled element 15 and anend edge in the width direction of the apex 17 b of the circular body 13match.

With the stent 11 having such a structure, superior conformability anddiameter reduction are realized, and thus damage to the stent due to themetallic fatigue hardly occurs. The knob portion 19 provided at the apex17 b of the waveform element 17 of the circular body 13 of the stent 11exerts an effect of reducing metallic fatigue. The slit 21 extendingfrom an inner peripheral portion of the apex 17 b of the waveformelement 17 of the circular body 13 of the stent 11 exerts an effect ofimproving diameter reduction of the stent 11.

Structurally speaking, stents of the conventional closed cell structureslack flexibility, and thus there has been a risk of inhibiting bloodflow due to a stent buckling in a tortuous blood vessel. Furthermore, ifa stent is deformed locally, the deformation propagates not only in aradial direction RD of the stent, but also in the longitudinal axisdirection LD, a result of which the stent cannot be deformedindependently and locally. For this reason, the stent cannot be adaptedto a complicated blood vessel structure such as an aneurysm and causes aspace between a peripheral wall of the stent and a blood vessel wall, aresult of which the stent easily slides in an intravascular lumen due tothe deformation accompanied with the pulsation of a blood vessel, andmay also cause movement (migration) of the stent after the placementtherein.

On the other hand, when the stent 11 according to the embodiment isdeformed from an expanded state to a radially reduced state (a crimpedstate), the wavy-line pattern of the circular body 13 is folded so as toenter a compressed state, and the coiled element 15 is made to be laidin the longitudinal axis direction LD as a coiled spring and enters astate being pulled in the longitudinal axis direction LD. When viewing asingle piece of the waveform element 17 of the wavy-line pattern of thecircular body 13 of the stent 11, as illustrated in FIG. 5, the waveformelement 17 deforms to be open and closed such as a tweezer upon thediameter reduction and expansion of the stent 11.

In a case in which the slit 21 is not provided at a valley side portionof a base of the waveform element 17 (an inner peripheral portion of theapex 17 b) as shown in FIG. 6A, when deforming the stent 11 so as toclose the waveform element 17 to radially reduce the stent 11, centerportions of the leg portions 17 a swell outward in a barrel-like shapeand thus easily deform, as illustrated in FIG. 6B. If the waveformelement 17 is swollen in a barrel-like shape in this way, the swollenportions in a barrel-like shape of the leg portions 17 a of the adjacentwaveform elements 17 in a circumferential direction in the circular body13 come into contact with each other when radially reducing the stent11.

This contact prevents the stent 11 (more specifically, the circular body13) from radially reducing, which leads to the degradation of the ratioof diameter reduction. On the other hand, the slit 21 is provided at abase portion of the waveform element 17 of the circular body 13 asillustrated in FIG. 7A in the stent 11 according to the embodiment.Therefore, when radially reducing the stent 11, as illustrated in FIG.7B, the stent 11 is deformed so that the leg portions 17 a of thewaveform element 17 adjacent in a circumferential direction in thecircular body 13 bring less contact with each other, a result of whichthe ratio of diameter reduction can be improved.

As described above, the waveform element 17 deforms to be open andclosed such as a tweezer upon the diameter reduction and expansion ofthe stent 11 as shown in FIG. 5. Therefore, upon crimping and expansionof the stent 11, the deformation concentrates on the apex so that thestrain due to material deformation occurs intensively at this part.Therefore, in a case of repeating diameter reduction and expansion ofthe stent 11 or in a case in which the stent 11 repeatedly receives loadaccompanied with deformation due to blood flow in a blood vessel orpulsation of a wall of a blood vessel, excessive metallic fatigue tendsto occur at the apex 17 b of the waveform element 17. Therefore, inorder to reduce the risk of metallic fatigue occurring, the shape of theapex 17 b is modified for an improvement in the stent 11 so as to reducethe strain occurring at the apex 17 b.

Upon diameter reduction and expansion of the stent 11, since thewaveform element 17 becomes opened and closed around a valley sideportion of the base portion (inner peripheral portion), the strain ofthe apex 17 b of the waveform element 17 occurs greatly particularly atan outer peripheral portion in the region of the apex 17 b (an outsideof the apex 17 b shown by a curve with arrows at the both ends of thecurve in FIG. 5). Here, the strain e is represented by the followingequation with the length before deformation being l₀ and the deformationamount being u.

e=u/l ₀

Therefore, in order to reduce the risk of metallic fatigue occurring atthe apex 17 b of the stent 11, it is only necessary to reduce the strainoccurring at the apex 17 b upon diameter reduction and expansion of thestent 11.

FIG. 8 is a partially enlarged view showing a first embodiment of anapex of a waveform element of the circular body of the stent. FIG. 9 isa partially enlarged view showing a second embodiment of an apex of awaveform element of the circular body of the stent. FIG. 10 is apartially enlarged view showing a third embodiment of an apex of awaveform element of the circular body of the stent.

When assuming that the same deformation amount u is imparted upondiameter reduction, it is possible to reduce the strain occurring at theapex 17 b by increasing the length corresponding to l₀. Furthermore, thedeformation of the waveform element 17 is made at a valley side portionof the base portion of the waveform element 17 (inner peripheralportion), and a portion that substantially contributes to thedeformation is a peak side portion of the apex 17 b of the waveformelement 17 (the range shown by a curve with arrows at both ends of thecurve on the upper side in FIGS. 8 to 10), specifically an outerperipheral portion. Therefore, as shown in FIGS. 8 to 10, it isconfigured in the stent 11 such that the knob portion 19 including theextension portion 19 a and the substantially semicircle portion 19 b andhaving a width greater than the width of the coiled element 15 is formedat the apex 17 b to allow the apex portion 17 b to extend in thelongitudinal axis direction LD.

More specifically, the extension portion 19 a extending in thelongitudinal axis direction LD is provided between the leg portions 17 aof the waveform element 17 and the substantially semicircle portion 19 bforming the apex 17 b so as to offset the apex 17 b outward from thevalley side portion of the base portion of the waveform element 17(inner peripheral portion) as a deformation base point. The outerperipheral portion of the apex 17 b is made to extend with such aconfiguration. In order to prevent adjacent knob portions 19 in acircumferential direction from blocking diameter reduction due to cominginto contact with each other upon diameter reduction, as shown in FIGS.8 to 10, it is desirable for the extension portion 19 a to be formed byway of a linear portion extending in the longitudinal axis direction LD.

It should be noted that, in a case in which the slit 21 extending fromthe inner peripheral portion of the apex 17 b is formed at the apex 17 bof the waveform element 17, as shown in FIGS. 7A and 7B, the deformationof the waveform element 17 takes place around a tip of the slit 21 (anupper end of the slit 21 in FIGS. 8 to 10). A main portion involved inthe deformation accompanied with crimping and expansion corresponds to aportion that is located more outside than the tip of the slit 21 of thewaveform element 17. Therefore, it is more preferable to configure suchthat the length of the extension portion 19 a is longer than the lengthof the slit 21 and the extension portion 19 a extends beyond the tip ofthe slit 21, as shown in FIG. 9, than to configure such that the lengthof the extension portion 19 a is the same as the length of the slit 21or shorter than the length of the slit 21, as shown in FIG. 8.

As shown in FIGS. 8 and 9, opposite side edges of the slit 21 are linearextending substantially in parallel. It should be noted that, as shownin FIG. 10, the opposite side edges of the slit 21 may not extendsubstantially in parallel (for example, the opposite side edges maybecome slightly wider toward the leg portions 17 a). In addition, theopposite side edges of the slit 21 may not be linear (not illustrated).

Furthermore, in a case of the stent 11 being formed of a super elasticalloy such as a nickel titanium alloy, as shown in FIG. 9, it can beconfigured so as to provide the knob portion 19 at the apex 17 b of thewaveform element 17 of the circular body 13 of the stent 11 and have thelength of the extension portion 19 a of the knob portion 19 longer thanthe length of the slit 21. With such a configuration, it is possible toextract the super elastic property of the super elastic alloy to amaximum extent and suppress a change in expansive force with respect toa change in the outer diameter of the stent 11.

In a case in which the slit 21 is provided at the apex 17 b of thewaveform element 17 of the circular body 13 of the stent 11, it isconfigured such that the length of the extension portion 19 a of theknob portion 19 provided at the apex 17 b is longer than the length ofthe slit 21 so that the volume ratio of the phase transformation tomartensite phase at a neighboring portion of the slit 21 upon loadingincreases. Therefore, it is configured for the stent 11 to include thewaveform element 17 having the apex 17 b as shown in FIG. 9, so that itis possible to realize the stent 11 for which a change in expansiveforce with respect to a change in a diameter of the stent 11 is gentleand with less change in expansive force with different diameters ofblood vessels.

The curve portion 15 a provided at both ends of the coiled element 15 ofthe stent 11 makes the deformation of the coiled element 15 at theconnected portion with the circular body 13 further smoother, a resultof which it exerts an effect of further improving the diameter reductionof the stent 11.

When radially reducing the stent 11, the coiled element 15 is deformedso as to elongate in the longitudinal axis direction LD. Therefore, inorder to improve the flexibility of the stent 11, it is necessary todesign the stent 11 so that the connecting portion of the apex 17 b ofthe circular body 13 and the coiled element 15 becomes flexible. Instent 11, the curve portion 15 a having a circular shape at both ends ofthe coiled element 15 is provided and the apex 17 b of the circular body13 is connected with the coiled element 15 via the curve portion 15 a.Upon the diameter reduction of the stent 11, the curve portion 15 a isbent and deformed, a result of which the flexible deformation of thecoiled element 15 becomes possible, which leads to an improvement indiameter reduction.

Furthermore, the configuration in which the tangential direction of thecurve portion 15 a at the connecting end at which the coiled element 15connects with the apex 17 b of the circular body 13 coincides with thelongitudinal axis direction LD exerts an effect of making a change inexpansive force with respect to a change in the diameter of the stent 11gentle.

The coiled element 15 is deformed like a coiled spring to elongate inthe longitudinal axis direction LD, which allows for the deformation ina radial direction RD accompanied with the diameter reduction of thestent 11. Therefore, by matching the tangential direction of the curveportion 15 a at the connecting end at which the circular body 13connects with the coiled element 15 with the longitudinal axis directionLD, it becomes possible to effectively exhibit deformation properties ofthe coiled element 15 in the longitudinal axis direction LD. Since it isconfigured such that the coiled element 15 can be deformed smoothly inthe longitudinal axis direction LD, the diameter reduction and expansionof the stent 11 is facilitated. Furthermore, since natural deformationin the longitudinal axis direction LD of the coiled element 15 isfacilitated, it is possible to prevent unpredictable deformationresistance from occurring, which exerts an effect of making the responseof expansive force with respect to a change in the diameter of the stent11 gentle.

The stent 11 is inserted into a catheter in a state of being radiallyreduced, extruded by an extruder such as a pusher and moved in thecatheter, and expanded at a site of pathology. At this moment, the forcein the longitudinal axis direction LD applied by the extruder interactsbetween the circular body 13 and the coiled element 15 of the stent 11to propagate over the entire stent 11.

The stent 11 having the abovementioned structure is produced bylaser-machining a material having biocompatibility, and more preferably,a tube made of a super elastic alloy. When producing a stent made of asuper elastic alloy tube, in order to reduce production cost, it ispreferable to produce the stent 11 by expanding an approximately 2 to 3mm tube to a desirable diameter and performing shape-memory treatmentafter laser-machining. However, the method of producing the stent 11 isnot limited to laser-machining and includes other methods such ascutting processing.

Next, an operational effect according to the configuration of “whenviewing in the radial direction RD perpendicular to the axial directionLD, the circular direction CD of the circular bodies 13 is inclined withrespect to the radial direction RD.” is explained. First, theconfiguration of the stent 11 is described in which, when viewing in theradial direction RD, the circular direction CD of the circular body 13follows the radial direction RD (not inclined with respect to the radialdirection RD).

FIG. 11A shows a central axis of a cross section of the stent and a sideview of a blood vessel. FIG. 11B is a schematic view of a cross sectionof the stent where the central axis is not displaced. FIG. 11C is aschematic view of a cross section of the stent where the central axis isdisplaced. FIG. 12 is a schematic view showing a malapposition. FIG. 13is a schematic view of a developed view of a highly flexible stent in anunloaded state according to a first embodiment of the present invention.FIG. 14 is a schematic view showing the behavior of a coiled element andthe center of the figure when the stent shown in FIG. 13 is bent. FIG.15 is a schematic view showing a behavior of the center of the figure ofa cross section of the stent bent. FIG. 16 is a schematic view showing abehavior in a case in which a distortion in a right-hand direction isapplied to the stent shown in FIG. 13. FIG. 17 is a schematic viewshowing a behavior in a case in which a distortion in a left-handdirection is applied to the stent shown in FIG. 13. FIGS. 18A to 18F isa schematic view showing a behavior of a distorted deformation in a caseof assuming a deformation with a coiled element of a stent as a part ofa left-hand spring structure. FIG. 19 is a developed view of aconventional stent in which a circular direction of a circular body isnot inclined with respect to a radial direction. FIG. 20 is a developedview showing a state after bending deformation being applied to thestent shown in FIG. 19.

Regarding a stent 110 (refer to FIG. 19) with a structure in which thecircular direction CD of the circular body 13 is not inclined withrespect to the radial direction RD, in an intracranial blood vessel,which is strongly curved, the center axis CL of a cross section of thestent 11 (110) is easily displaced, as shown in FIG. 11A to 11C. Itshould be noted that, in each drawing, a solid line indicates a bloodvessel BV, a dashed-dotted line indicates the center axis CL of thestent 11 (110), and a dashed line indicates a cross section of the stent11 (110).

In FIG. 19, a position at the center of the figure of the cross sectionof the circular body 13 is shown by a black circle. A line passingthrough the centers of the figures (black circles) of the cross sectionsof each circular body 13 corresponds to the center axis CL of the stent110. Each of the circular bodies 13 are denoted by (A), (B), and (C)from the left in the figure. The coiled elements 15 connected with theadjacent circular bodies 13, 13 are denoted by (A′) and (B′) from theleft in the figure. When bending load is applied to the abovementionedstent 110, a back side portion of the stent 110 exhibits a deformationbehavior as if being pulled in the axial direction LD.

In FIG. 20, when bending is applied to the stent 110, the circular body13(B) moves in a circumferential direction. This is due to the coiledelements 15 connecting between the circular body 13(A) and the circularbody 13(B) or between the circular body 13(B) and the circular body13(C) being pulled and expanded so as to move the circular body 13(B) inthe direction of the white arrow. In this way, the center of the figurebefore the deformation (white circle) moves to the position of the blackcircle after the deformation. At this time, as shown in FIG. 20, thecenter axis CL passing through the centers of figures shown by the blackcircles in each of the circular bodies 13(A), 13(B), and 13(C) afterdeformation becomes zigzagged. This causes the center of the figure tomove to a displaced position from the center of the cross section of ablood vessel when the stent 110 is bent. At this time, if the center ofthe figure of the cross section of the stent becomes displaced from thecenter of the cross section of the blood vessel, a strut of the stentfloats from a blood vessel wall BV (generation of malapposition).

If the center of the figure of the cross section of the stent 11 isdisplaced when the stent 11 is bent, the adhesion of the stent 11 to theblood vessel wall BV decreases, which causes malapposition (refer toFIG. 12). The displacement of the center of the figure of the crosssection of the stent 11 is caused by transmission of a force workingtowards the circumferential direction. Malapposition refers to a strutof the stent 11 floating (moving away) from the blood vessel wall BV asshown in FIG. 12.

Stagnation of blood flow occurs between the stent 11 and the bloodvessel wall BV, which leads to the generation of a blood clot. Due tothis, blood clots are generated excessively at an intravascular lumen ofthe stent 11 (in-stent restenosis) or the blood clots flow to a terminusthereof, a result of which it is likely that problems such as blockagein a blood vessel will occur. (Background Incidence of LateMalapposition After Bare-Metal Stent Implantation, etc.) Furthermore,since the stress distribution of the stent 11 differs locally, the riskof damaging a blood vessel wall, etc., increases.

As shown in FIGS. 13 and 14, when the coiled element 15 (B′) is pulledin a circumferential direction of (a), in order to correct for thematter of being pulled in the circumferential direction of (a), thecircular body 13 (A) tries to deform the circular body 13 (B) in adirection of (b). For this reason, as a result, since the center of thefigure also moves in the axial direction LD (moving from the blackcircle to a white circle), as shown in FIG. 15, it is possible to reducemalapposition due to the displacement of the center of the figure.

On the other hand, in regard to the stent 11 of the present embodiment,since the circular body 13 having the wavy-line pattern can be easilydeformed in a circumferential direction, the stent 11 can be flexiblyadapted to contraction and expansion in a radial direction. Furthermore,the coiled element 15 connecting between the adjacent circular bodies13, 13 extends in a spiral manner around the central axis and isdeformed like a coiled spring. For this reason, when the stent 11 isbent, the coiled element 15 elongates at the outside of a bent portionand contracts at the inside of the bent portion. With such aconfiguration, flexible bending deformation of the overall stent 11 inthe longitudinal axis direction LD is made possible.

Furthermore, an external force given to the stent 11 locally and aresulting deformation propagate in a radial direction RD by way of thecircular body 13 of the wavy-line pattern and propagate in acircumferential direction by way of the coiled element 15. Therefore,the circular body 13 and the coiled element 15 can be deformed almostindependently at each site. With such a configuration, the stent 11 canbe placed so as to be adapted to a site of pathology in a blood vesselstructure even in a case in which the stent 11 is adapted to a site ofpathology in a particular blood vessel such as a brain aneurysm. Forexample, in a case in which the stent 11 is placed at the site of abrain aneurysm, the circular body 13 of the wavy-line pattern is placedat a neck portion of a knob. In this way, the circular body 13 expandsin a radial direction RD and develops in a space of the knob, so thatthe stent 11 can be fastened securely at this site.

Furthermore, the coiled element 15 is in contact with a peripheral wallof a blood vessel along a shape of the blood vessel wall so as to serveas an anchor. Therefore, the risk of the stent 11 migrating is reduced.Furthermore, since the stent 11 has a closed cell structure, even whenit is adapted to a bent site, it is possible to reduce the risk of thestrut of the stent 11 protruding outward in a flared shape to damage ablood vessel wall and the strut of the stent 11 causing inhibition ofblood flow.

Furthermore, as shown in FIG. 16, when a left-handed distortion isapplied to the stent 11, a force acts in such a manner that the onecoiled element 15 (A′) is pulled in a perpendicular direction withrespect to the cross section of an element wire of a spring. For thisreason, the element wire is deformed so as to be wound in a direction of(d) in FIG. 16 (i.e. in the circumferential direction) and exhibits thebehavior of being radially reduced in the radial direction RD. On theother hand, a force acts in such a manner that the other coiled element15 (B′) is compressed in a perpendicular direction with respect to thecross section of the element wire of a spring. For this reason, theelement wire is deformed so as to be pulled away in a direction of (e)in FIG. 16 (i.e. in the circumferential direction) and, as a result,exhibits the behavior of a diameter being expanded in a radial directionRD. As a result, since the deformations of the one coiled element 15(A′) and the other coiled element 15 (B′) at each unit are compensatedby each other, the deformation amount in the radial direction RD of thecoiled element 15 in the stent 11 as a whole is suppressed.

On the other hand, as shown in FIG. 17, when a right-handed distortionis applied to the stent 11, a force acts in such a manner that the othercoiled element 15 (B′) is pulled in a perpendicular direction withrespect to the cross section of the element wire of a spring. For thisreason, the element wire is deformed so as to be wound in the directionof (f) of FIG. 17 (i.e. in the circumferential direction) and exhibitsthe behavior of being radially reduced in the radial direction RD. Onthe other hand, a force acts in such a manner that the other coiledelement 15 (A′) is compressed in a perpendicular direction with respectto the cross section of the element wire of a spring. For this reason,the element wire is deformed so as to be pulled away in the direction of(g) in FIG. 17 (i.e. in the circumferential direction) and, as a result,exhibits the behavior of a diameter being expanded in a radial directionRD. As a result, since the deformations of the one coiled element 15(A′) and the other coiled element 15 (B′) are compensated by each other,the deformation amount in the radial direction RD of the coiled element15 in the stent 11 as a whole is suppressed.

In this way, by introducing the coiled element 15R and 15L (15 (A′), 15(B′)) of which the winding directions are opposite to each other, it ispossible to reduce the difference in the deformation amounts in theradial direction RD between the left and right distorted deformations.

Furthermore, in the present embodiment, the length of the coiled element15 is shorter than the length of the leg portion 17 a or not too long.For this reason, as compared with the case in which the length of thecoiled element 15 is considerably longer than the length of the legportion 17 a, when being distorted in a direction opposite to thewinding direction of the coiled element 15, it is not likely that thestent 11 swells as a whole, a result of which malapposition is lesslikely to occur. Furthermore, since there are few portions at which theforce in the radial direction RD in the stent 11 does not act, withregards to the distribution of the force in the radial direction RD inthe stent 11, cells at which a high force acts locally and portions atwhich a force substantially becomes 0 (zero) locally are less likely tooccur.

Regarding the materials for a stent, a material having high rigidity andhigh biocompatibility in itself are preferable. Such materials include,for example, titanium, nickel, stainless steel, platinum, gold, silver,copper, iron, chrome, cobalt, aluminum, molybdenum, manganese, tantalum,tungsten, niobium, magnesium, and calcium, or alloys including these.Furthermore, for such materials, synthetic resin materials such aspolyolefins such as PE and PP, polyamide, polyvinyl chloride,polyphenylene sulfide, polycarbonate, polyether, and polymethylmethacrylate can be used. Furthermore, for such materials, biodegradableresins such as polylactic acid (PLA), polyhydroxybutyrate (PHB),polyglycolic acid (PGA) and polyε-caprolactone can be used.

Among these, titanium, nickel, stainless steel, platinum, gold, silver,copper and magnesium or alloys including these are preferable. Alloysinclude, for example, Ni—Ti alloy, Cu—Mn alloy, Cu—Cd alloy, Co—Cralloy, Cu—Al—Mn alloy, Au—Cd—Ag alloy and Ti—Al—V alloy. Furthermore,alloys include, for example, alloys of magnesium with Zr, Y, Ti, Ta, Nd,Nb, Zn, Ca, Al, Li and Mn. Among these alloys, Ni—Ti alloy ispreferable.

A stent may include a medical agent. Here, a stent including a medicalagent refers to the matter of the stent releasably supporting a medicalagent so that the medical agent can be eluted. Although the medicalagent is not limited, a physiologically active substance can be used,for example. Physiologically active substances include, for example,drugs for suppressing intimal hyperplasia, anticancer drugs, animmune-suppressing drugs, antibiotic drugs, antirheumatic drugs,antithrombogenic drugs, HMG-CoA reductase inhibitors, ACE inhibitors,calcium antagonist agents, antilipemic drugs, anti-inflammatory drugs,integrin inhibitors, antiallergic agents, antioxidant agents, GPIIbIIIaantagonist drugs, retinoid, flavonoid, carotenoid, lipid improvers,inhibitors of DNA synthesis, tyrosine kinase inhibitors, antiplateletdrugs, vascular smooth muscle growth inhibitors, anti-inflammatoryagents, interferons, etc. It is also possible to use a plurality ofthese drugs.

“A drug for suppressing intimal hyperplasia” to prevent recurrentstenosis is preferable in particular. A drug for suppressing intimalhyperplasia includes, for example, a drug possessing an effect ofsuppressing blood vessel intimal hyperplasia that does not inhibit thegrowth of endothelial cells. Such a drug includes, for example,Argatroban;(2R,4R)-4-methyl-1-[N2-((RS)-3-methyl-1,2,3,4-tetrahydro-8-quinolinesulfonyl)-L-arginine]-2-piperidinecarboxylicacid (Japanese Unexamined Patent Application, Publication No.2001-190687; International Publication No. WO2007/058190), Ximelagatran,Melagatoran, Dabigatran, Dabigatran etexilate, rapamycin, everolimus,biolimus A9, zotarolimus, tacrolimus, paclitaxel, statin, etc.

In order for the stent to involve a drug, the surface of the stent maybe coated with the drug. In this case, the surface of the stent may bedirectly coated with a drug, or the stent may be coated with polymer inwhich a drug is contained. Furthermore, grooves or holes for storing adrug in a stent may be provided as a reservoir, and the drug or amixture of the drug and polymer may be stored therein. A reservoir forstorage has been disclosed in Japanese Unexamined Patent Application(Translation of PCT Publication), Publication No. 2009-524501.

The polymers used in this case include, for example, flexible polymershaving a glass transition temperature of −100° C. to 50° C. such assilicone rubber, urethane rubber, fluorine resin, polybutyl acrylate,polybutyl methacrylate, acrylic rubber, natural rubber, ethylene-vinylacetate copolymer, styrene-butadiene block copolymer, styrene-isopreneblock copolymer and styrene-isobutylene block copolymer, andbiodegradable polymers such as polylactic acid, poly(lacticacid-glycolic acid), polyglycolic acid, poly(lacticacid-ε-caprolactone), poly(glycolic acid-trimethylene carbonate) andpoly-β-hydroxybutyric acid.

The mixture of polymer and a drug can be performed by dispersing thedrug in polymer, for example, and can be performed following thedisclosure of PCT International Publication No. WO2009/031295. A drugcontained in a stent is delivered to an affected area via the stent andreleased in a controlled manner.

It is possible to coat a diamond like carbon layer (DLC layer) on thesurface of a stent. The DLC layer may be a DLC layer including fluorine(F-DLC layer). In this case, it becomes a stent that excels inantithrombogenicity and biocompatibility.

Next, a method of using the stent 11 is described. A catheter isinserted into a blood vessel of a patient and the catheter is deliveredto a site of pathology. Then, the stent 11 is radially reduced (crimped)and placed in the catheter. The property of the diameter reduction ofthe stent 11 is improved by multiple and synergistic effects due to thewavy-line pattern of the circular body 13, the slit 21 formed at theapex 17 b of the circular body 13, the curve portion 15 a of the coiledelement 15, and the configuration in which a tangential direction of thecurve portion 15 a at a connecting end coincides with the longitudinalaxis direction LD. Therefore, it becomes easier to insert the stent 11into a narrow catheter and also becomes possible to apply the stent 11to narrower blood vessels, as compared to conventional stents.

Next, the stent in a state of being radially reduced is pushed out alonga lumen of the catheter using an extruder such as a pusher and the stent11 is extruded from a tip of the catheter and expanded at a site ofpathology. The flexibility upon delivery of the stent 11 is improved bymultiple and synergistic effects due to the configuration in which aplurality of the circular bodies 13 are connected with the coiledelements 15, the curve portion 15 a of the coiled element 15, and theconfiguration in which a tangential direction of the curve portion 15 aat a connecting end coincides with the longitudinal axis direction LD.Therefore, even in a case in which the catheter is inserted into atortuous blood vessel, the stent 11 is deformed flexibly along thecatheter and the stent 11 can be easily delivered to a site ofpathology.

Moreover, by configuring so that the stent 11 has the knob portion 19provided at the apex 17 b of the circular body 13, it is possible tosuppress the occurrence of metallic fatigue, and thus it is possible tosuppress the damage to the stent 11 due to the repetition of diameterreduction and expansion of the stent 11 caused by misplacement andcyclic deformations of the stent 11 caused by a blood flow or apulsating movement of a blood vessel, etc.

In addition, the flexibility of the stent 11 is improved by multiple andsynergistic effects due to the configuration in which the region inwhich the phase transformation is caused to martensite phase at adeformation portion upon crimping increasing by providing the slit 21 atthe apex 17 b of the circular body 13, the curve portion 15 a of thecoiled element 15, and the configuration in which a tangential directionof the curve portion 15 a at a connecting end coincides with thelongitudinal axis direction LD, and the change in expansive force withrespect to the change in the diameter of the stent 11 becomes gentle inthe unloading process. As a result of this, the conformability of thestent 11 can be improved and it is also possible to place the stent 11at a site where the diameter of a blood vessel changes locally such as atapered blood vessel, without placing an unnecessary load on the bloodvessel.

Next, other embodiments of the present invention are described. Foraspects which are not described specifically in the other embodiments,the explanations for the first embodiment are applied as appropriate.Effects similar to the first embodiment are exerted in the otherembodiments as well. FIG. 21 is a developed view showing a stent 11Aaccording to a second embodiment of the present invention to bevirtually expanded into a plane.

As shown in FIG. 21, the stent 11A according to the second embodimenthas substantially the same mesh pattern as the stent 11 according to thefirst embodiment shown in FIG. 2. In FIG. 21, the symbols Δ (triangle)that overlap in the radial direction RD (refer to a dashed-two dottedline L20 in FIG. 21) or the symbols □ (square) that overlap in theradial direction RD indicate joining points.

The stent 11A according to the second embodiment has a single spiralstructure. As shown in FIG. 21, the single spiral structure is astructure in which there is a single spiral L28 between the joiningpoints Δ (triangle) in the reference line L20 extending in the radialdirection RD. The wavy-line pattern of a circular body 13 is a zigzaggedshape. A virtual line L29 passing through a plurality of apices 17 b onthe same side of the zigzagged shape is linear.

It should be noted that the stent 11A according to the second embodimentshown in FIG. 21 and the stent 11 according to the first embodimentshown in FIG. 2 are in a mirror image relationship in the axialdirection LD. X(1), X(2), X(3), and X(4) in FIG. 21 are used forexplaining modified examples described later.

In the stent 11 according to the first embodiment shown in FIG. 2 andthe stent 11A according to the second embodiment shown in FIG. 21, thewavy-line pattern body 13 forms a circular body. On the other hand, inthe present invention, a wavy-line pattern body 13 can be adopted whichis non-continuous in a circumferential direction and does not form acircular body. Compared with the wavy-line pattern body that forms acircular body, the wavy-line pattern body 13 that does not form acircular body has a form in which one or a plurality of struts (legportions 17 a) that constitutes a wavy-line pattern body is omitted.Specific embodiments from a first modified example to a fourth modifiedexample are described in detail below.

FIG. 22 is a developed view showing a stent 11A-1 according to a firstmodified example of the second embodiment of the present invention to bevirtually expanded into a plane. The stent 11A-1 of the first modifiedexample has a form in which a plurality of struts including a strut (legportions 17 a) to which X(1) is added in FIG. 21 is omitted. Thedashed-two dotted line L21 shows a virtual line along a plurality ofstruts (leg portions 17 a) omitted.

FIG. 23 is a developed view showing a stent 11A-2 according to a secondmodified example of the second embodiment of the present invention to bevirtually expanded into a plane. The stent 11A-2 of the second modifiedexample has a form in which a plurality of struts including a strut (legportions 17 a) to which X(2) is added in FIG. 21 is omitted. Thedashed-two dotted line L22 shows a virtual line along a plurality ofstruts (leg portions 17 a) omitted.

FIG. 24 is a developed view showing a stent 11A-3 according to a thirdmodified example of the second embodiment of the present invention to bevirtually expanded into a plane. The stent 11A-3 of the third modifiedexample has a form in which a plurality of struts including a strut (legportions 17 a) to which X(3) is added in FIG. 21 is omitted. Thedashed-two dotted line L23 shows a virtual line along a plurality ofstruts (leg portions 17 a) omitted.

FIG. 25 is a developed view showing a stent 11A-4 according to a fourthmodified example of the second embodiment of the present invention to bevirtually expanded into a plane. The stent 11A-4 of the fourth modifiedexample has a form in which a plurality of struts including a strut (legportions 17 a) to which X(4) is added in FIG. 21 is omitted. Thedashed-two dotted line L24 shows a virtual line along a plurality ofstruts (leg portions 17 a) is omitted.

In the first modified example to the fourth modified example, the numberof struts to be omitted can be set as one or a plurality as appropriatein a range in which the shape of the stent 11 can be realized.

FIG. 26 is a developed view showing a stent 11A-5 according to a fifthmodified example of the second embodiment of the present invention to bevirtually expanded into a plane. In the stent 11A-5 of the fifthmodified example, struts (leg portions 17 a of a circular body 13,coiled elements 15) which are continuous in the axial direction LD,becomes thicker than the other struts, a result of which the rigidity ofthe thick continuous struts becomes higher than the other struts. Thethick continuous struts (in FIG. 26, its path is shown by the dashedline L251 or the dashed-two dotted line L252) serve as a backbone. Morethan one thick continuous strut can be provided to a single stent.

FIG. 27 is a developed view showing a stent 11A-6 according to a sixthmodified example of the second embodiment of the present invention to bevirtually expanded into a plane. In the stent 11A-6 of the sixthmodified example, first additional strut 31 a extending in a circulardirection CD are provided which connect the coiled elements 15 adjacentin the circular direction CD.

FIG. 28 is a developed view showing a stent 11A-7 according to a seventhmodified example of the second embodiment of the present invention to bevirtually expanded into a plane. In the stent 11A-7 of the seventhmodified example, second additional struts 31 b extending in a directionperpendicular to the circular direction CD are provided which connectcircular bodies 13 adjacent in a direction perpendicular to the circulardirection CD.

It should be noted that the shape of an additional strut, the locationof a strut to be provided, the number of struts to be provided, etc.,are not limited in particular. Both the first additional strut 31 a andthe second additional strut 31 b may be provided to a single stent 11.

FIG. 29 is a developed view showing a stent 11B according to a thirdembodiment of the present invention to be virtually expanded into aplane. The stent 11B according to the third embodiment has a doublespiral structure. As shown in FIG. 29, the double spiral structureindicates that there are two spirals of L31 and L32 between joiningpoints □ (square) at a reference line L30 extending in the radialdirection RD.

FIG. 30 is a developed view showing a stent 11C according to a fourthembodiment of the present invention to be virtually expanded into aplane.

In the stent 11B according to the third embodiment shown in FIG. 29, onecoiled element 15R and the other coiled element 15L are alternatelyarranged in an axial direction LD. All of the one coiled elements 15Rare homomorphic and all of the other coiled elements 15L arehomomorphic.

In the stent 11C according to the fourth embodiment shown in FIG. 30,the one coiled element 15R and the other coiled element 15L arealternately arranged in the axial direction LD. When focusing attentionon the one coiled elements 15R, one coiled element 15R1 and the othercoiled element 15R2 adjacent to each other are heteromorphic. The onecoiled elements 15R1 and the other coiled elements 15R2 are alternatelyarranged. When focusing attention on the other coiled elements 15L, theother coiled element 15L1 and the other coiled element 15L2 adjacent toeach other are heteromorphic. The other coiled element 15R1 and theother coiled element 15R2 are alternately arranged.

FIG. 31 is a developed view showing a stent 11D according to a fifthembodiment of the present invention to be virtually expanded into aplane. A mesh pattern of the stent 11D according to the fifth embodimentis substantially the same as the mesh pattern of the stent 11A accordingto the second embodiment shown in FIG. 21. A base end portion 25 side (aside of being connected with a guide wire 51) of the stent 11D accordingto the fifth embodiment is made narrow in a rod-like shape. In the fifthembodiment, three tip portions 27 (side opposite to the base end portion25) of the stent 11D are formed in a rod-like shape. The tip portions 27project in a rod-like shape in the axial direction LD from apices 17 bof the circular body 13.

FIGS. 32A to 32D are views showing the behavior of the stent 11Daccording to the fifth embodiment being pushed out from a catheter 41and expanded. In practice, the stent 11D is pushed out from a catheter41 inside a blood vessel and expanded. However, explanations areprovided here of the behavior of the stent 11D being pushed out from thecatheter 41 in an unconstrained state not inside of a blood vessel andexpanded. Since the stent 11D according to the present invention has theabovementioned structure, the stent 11D is pushed out from the catheter41 in a manner of rotating while swinging and expanded. When the stent11D having such a behavior is pushed out from the catheter 41 inside ofa blood vessel and expanded, the stent 11D cannot be swung. Instead, asshown in FIG. 33, the stent 11D is subject to dig into a blood clot BCthat has been trapped.

Furthermore, as shown in FIG. 33, in a state in which the stent 11D isexpanded, a strut is likely to be in a state of expanding in the axialdirection LD. With such a configuration, the performance of the stent11D trapping the blood clot BC (the performance of the stent 11D ofdigging into blood clot BC) and the conformability of the stent 11D to ablood vessel improve. According to the stent 11D of the presentinvention, the overall stent 11D can be reduced in diameter, theflexibility during diameter reduction is high, and the durability isalso high.

Next, a stent 11E according to a sixth embodiment of the presentinvention is described. FIG. 34 is a perspective view showing the stent11E according to the sixth embodiment of the present invention. FIG. 35is a view in which the stent 11E in FIG. 34 is seen in an axialdirection. Compared with the first embodiment, the sixth embodimentmainly differs in the cross-sectional shape of the stent.

As shown in FIGS. 34 and 35, the cross sectional shape of the stent 11Eaccording to the sixth embodiment is a substantially triangular shape.Each of the triangle-shape apices 23 is rounded. Each of thetriangle-shape apices 23 is aligned in an axial direction LD in such amanner of being spirally displaced in the dashed line direction shown inFIG. 34. It should be noted that each of the triangle-shape apices 23may be aligned linearly. The substantially triangular shape may besimilar forms in the axial direction LD or may not be similar forms. Theshape of each side 24 forming the triangular shape may be linear orcurved.

The stent 11E having a cross sectional shape of a substantiallytriangular shape can be obtained as follows, for example. Similarly tothe forming method of a stent having a normal cross sectional shape(circular shape, oval shape, and shapes similar thereto), cutoutmachining is performed by way of laser-machining from a tube. Then, thetube on which the cutout machining was performed is formed to be in across section of a substantially triangular shape.

According to the sixth embodiment having a substantially triangularcross sectional shape, it is possible to reduce friction between a bloodvessel wall and the stent 11E upon recovery of the stent 11E.Furthermore, by reducing a contact space of the stent 11E with respectto a blood vessel wall, it is possible to reduce friction between ablood vessel wall and the stent 11E upon recovery of the stent 11E.

FIG. 36 is a developed view showing a stent 11F according to a seventhembodiment of the present invention to be virtually expanded into aplane. As shown in FIG. 36, virtual lines L29-2 and L29-3 passingthrough a plurality of apices 17 b on the same side of the zigzaggedshape of the wavy-line pattern of the circular body 13 are non-linear.The non-linear line includes, for example, a curve having one flexionpoint (refer to FIG. 36) or a curve having a plurality of flexion points(not shown). In a case of the aspect shown in FIG. 36, the shape of an“area surrounded by struts” S11 and the shape of an area S12 adjacent toeach other in the circular direction CD differ. Similarly, the shape ofan “area surrounded by struts” S21 and the shape of an area S22 adjacentto each other in the circular direction CD differ.

FIG. 37 is a developed view showing various modified examples of coiledelements 15. As shown in FIG. 37, a coiled element 15-1 has a greaterflexion rate (curvature) than that of the coiled element 15 shown inFIG. 3. A coiled element 15-2 has a greater extent of bending(curvature) than that of the coiled element 15-1. A coiled element 15-3has a curve which projects in a direction perpendicular to the circulardirection CD as well. A coiled element 15-4 has a curve having fourflexion points.

FIG. 38 is a view showing a modified example of the shape of aconnecting portion of a coiled element 15 and an apex 17 b of a circularbody 13 (corresponding to FIG. 4). As shown in FIG. 38, the center in awidth direction of an end of the coiled element 15 and an apex (thecenter in a width direction) of the apex 17 b of the circular body 13match. An end edge in the width direction of the end of the coiledelement 15 and an end edge in the width direction of the apex 17 b ofthe circular body 13 are displaced from each other (do not match).

Next, a connecting structure of a highly flexible stent of the presentinvention and a guide wire is described. FIG. 39 is a cross sectionalview showing a connecting portion of the stent 11D of the presentinvention and a guide wire 51. As shown in FIG. 39, a tip portion 53 ofthe guide wire 51 is joined with a base end portion 25 of the stent 11D.The tip portion 53 of the guide wire 51 is made narrow to be in atapered shape. Inner coiled springs 55 are extrapolated at an areaadjacent to the base end portion 25 of the stent 11D at the tip portion53 of the guide wire 51.

Outer coiled springs 57 are extrapolated across the base end portion 25of the stent 11D, the inner coiled springs 55, and an area adjacent tothe inner coiled springs 55 at the tip portion 53 of the guide wire 51.In other words, a double spring composed of the inner coiled springs 55and the outer coiled springs 57 is provided. Regarding one end portionof the outer coiled springs 57, its movement in the axial direction LDis restricted due to an expanded portion of the stent 11D. Regarding theother end portion of the outer coiled springs 57, its movement in theaxial direction LD is restricted due to a welded portion 59 whichbecomes thick at an outer circumference of the tip portion 53 of theguide wire 51 being joined with the tip portion 53 of the guide wire 51.

FIG. 40 is a cross sectional view showing the tip portion 27 of thestent 11D of the present invention. Coiled springs 29 are extrapolatedat the rod-like tip portion 27. A tip end of the tip portion 27protrudes from the coiled springs 29.

Materials for each coiled spring are described. The material for theouter coiled springs 57 is not specifically limited so far as being amaterial that can form a coil, and includes, for example, stainlesssteel (SUS). Materials for the inner coiled springs 55 and the coiledsprings 29 are preferably materials that are radio-opaque and can form acoil. With such materials, the inner coiled springs 55 and the coiledsprings 29 serve as a marker that is a mark upon surgery. Thesematerials include platinum-iridium (Pt—Ir) alloy.

The joining method of the coiled springs 29 and the tip portion 27 ofthe stent 11D is not specifically limited so far as being a joiningmethod used for a medical device such as welding, UV adhesion andinfiltration of silver solder.

The welding method includes, for example, a method of adhesively fixingby melting the coiled springs 29 and the tip portion 27 of the stent11D, and a method of melting an area that projects from the coiledsprings 29 at the tip portion 27 of the stent 11D thereby restrictingthe movement of the coiled springs 29.

In the case of UV adhesion, the coiled springs 29 are fixed at the tipportion 27 of the stent 11D using radiation curing polymer of medicalgrade. The procedure includes: applying liquid curing polymer to the tipportion 27 of the stent 11D; and after the coiled springs 29 are placedthereon, promoting the curing of the liquid curing polymer by applyingradiation thereto, thereby fixing the coiled springs 29 to the tipportion 27 of the stent 11D.

In the case of infiltration of silver solder, the coiled springs 29 areformed from a material different from that of the stent 11D, and silversolder, etc. is infiltrated to the coiled springs 29 from above, therebyfixing the coiled springs 29 to the tip portion 27 of the stent 11D.

Although the stents according to the present invention are describedwith reference to the illustrated embodiments, the present invention isnot limited to the illustrated embodiments. For example, the length ofthe one coiled element 15R may be equivalent to the length of the othercoiled element 15L. Both the length of the one coiled element 15R andthe length of the other coiled element 15L may be longer than the lengthof the leg portion 17 a or shorter than the length of the leg portion 17a. The spiral direction of the coiled element 15 may be right-handed orleft-handed.

1. A highly flexible stent comprising: a plurality of wavy-line patternbodies having a wavy-line pattern and arranged side-by-side in an axialdirection; and a plurality of coiled elements arranged between thewavy-line pattern bodies that are adjacent and extending in a spiralmanner around an axis, wherein all apices on opposite sides of thewavy-line pattern of the wavy-line pattern bodies that are adjacent areconnected by way of the coiled elements, wherein, when viewing in aradial direction perpendicular to the axial direction, a circulardirection of the wavy-line pattern bodies is inclined with respect tothe radial direction, and wherein a winding direction of one of thecoiled elements located at one side in the axial direction with respectto the wavy-line pattern bodies and a winding direction of one other ofthe coiled elements located at the other side in the axial direction areopposite.
 2. The highly flexible stent according to claim 1, wherein anangle at which the circular direction of the wavy-line pattern bodiesinclines with respect to the radial direction is 30° to 60°.
 3. Thehighly flexible stent according to claim 1, wherein the wavy-linepattern bodies form a circular body by connecting, in a circumferentialdirection, a plurality of waveform elements of substantially V-shapemade by coupling two leg portions at an apex, and wherein the length ofthe one of the coiled elements is longer than the length of the legportion and the length of the one other of the coiled elements isshorter than the length of the leg portion.
 4. The highly flexible stentaccording to claim 3, wherein the length of the one of the coiledelements is no more than 1.5 times the length of the leg portion.
 5. Thehighly flexible stent according to claim 1, wherein the wavy-linepattern bodies are non-continuous in a circumferential direction and donot form a circular body, and have a shape in which one or a pluralityof struts that constitutes the wavy-line pattern bodies is omitted, ascompared with the wavy-line pattern bodies that form a circular body. 6.The highly flexible stent according to claim 1, wherein a crosssectional shape is a substantially triangular shape.